linux-kernel - Re: [PATCH 2/2] drivers/amba: probe via device tree

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Date:	Mon, 23 May 2011 09:23:54 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Stephen Neuendorffer <stephen.neuendorffer@...inx.com>,
	Kevin Hilman <khilman@...com>,
	Segher Boessenkool <segher@...nel.crashing.org>,
	Arnd Bergmann <arnd@...db.de>,
	devicetree-discuss@...ts.ozlabs.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 2/2] drivers/amba: probe via device tree

On Sat, May 21, 2011 at 5:47 PM, Russell King - ARM Linux
<linux@....linux.org.uk> wrote:
> On Sat, May 21, 2011 at 11:42:34AM -0600, Grant Likely wrote:
>> Russell, it seems to me that the primary behaviour that amba_bus has
>> over platform_bus is the clock management, and secondarily
>> verification of the type of device by the device id.  Am I correct, or
>> am I missing something?
>
> It matches by vendor/device ID just like PCI does, and does the bus
> clock management and power management in a really nice way, which I
> doubt platform devices will ever do.
>
> The way this discussion is going, I'm going to suggest that we also
> convert PCI stuff to being platform devices too.  I don't see the
> point of PCI existing for all the same reasons being given in this
> thread.

I certainly don't see that as being the direction this discussion is going.

I see a serious question about how best to model AMBA primecell
devices in the device tree, and a similarly serious question about
whether to instantiate them as platform_devices or amba_devices.
Modelled behaviour in this case (clock/power management) is
particularly important, and you're right, platform_devices will never
implement that behaviour in the core code (this issue has already been
pushed back on; see discussions about omap_device).

g.
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